Improve code for DocFragment rework

Author: GuillaumeGomez

src/librustdoc/clean/types.rs

@@ -486,6 +486,13 @@ crate enum DocFragmentKind {
     Include { filename: Symbol },
 }
 
+// The goal of this function is to apply the `DocFragment` transformations that are required when
+// transforming into the final markdown. So the transformations in here are:
+//
+// * Applying the computed indent to each lines in each doc fragment (a `DocFragment` can contain
+//   multiple lines in case of `#[doc = ""]`).
+// * Adding backlines between `DocFragment`s and adding an extra one if required (stored in the
+//   `need_backline` field).
 fn add_doc_fragment(out: &mut String, frag: &DocFragment) {
     let s = frag.doc.as_str();
     let mut iter = s.lines().peekable();
@@ -792,11 +799,14 @@ impl Attributes {
         if out.is_empty() { None } else { Some(out) }
     }
 
+    /// Return the doc-comments on this item, grouped by the module they came from.
+    ///
+    /// The module can be different if this is a re-export with added documentation.
     crate fn collapsed_doc_value_by_module_level(&self) -> FxHashMap<Option<DefId>, String> {
         let mut ret = FxHashMap::default();
 
         for new_frag in self.doc_strings.iter() {
-            let out = ret.entry(new_frag.parent_module).or_insert_with(|| String::new());
+            let out = ret.entry(new_frag.parent_module).or_default();
             add_doc_fragment(out, &new_frag);
         }
         ret
@@ -805,8 +815,7 @@ impl Attributes {
     /// Finds all `doc` attributes as NameValues and returns their corresponding values, joined
     /// with newlines.
     crate fn collapsed_doc_value(&self) -> Option<String> {
-        let s: String = self.doc_strings.iter().collect();
-        if s.is_empty() { None } else { Some(s) }
+        if self.doc_strings.is_empty() { None } else { Some(self.doc_strings.iter().collect()) }
     }
 
     /// Gets links as a vector

src/librustdoc/formats/cache.rs

@@ -314,10 +314,9 @@ impl DocFolder for Cache {
                             ty: item.type_(),
                             name: s.to_string(),
                             path: path.join("::"),
-                            desc: item.doc_value().map_or_else(
-                                || String::new(),
-                                |x| short_markdown_summary(&x.as_str()),
-                            ),
+                            desc: item
+                                .doc_value()
+                                .map_or_else(String::new, |x| short_markdown_summary(&x.as_str())),
                             parent,
                             parent_idx: None,
                             search_type: get_index_search_type(&item),

src/librustdoc/html/render/mod.rs

@@ -198,11 +198,7 @@ impl SharedContext<'_> {
     /// Based on whether the `collapse-docs` pass was run, return either the `doc_value` or the
     /// `collapsed_doc_value` of the given item.
     crate fn maybe_collapsed_doc_value<'a>(&self, item: &'a clean::Item) -> Option<String> {
-        if self.collapsed {
-            item.collapsed_doc_value().map(|s| s.to_string())
-        } else {
-            item.doc_value().map(|s| s.to_string())
-        }
+        if self.collapsed { item.collapsed_doc_value() } else { item.doc_value() }
     }
 }
 
@@ -2196,7 +2192,7 @@ fn item_module(w: &mut Buffer, cx: &Context<'_>, item: &clean::Item, items: &[cl
                 let stab = myitem.stability_class(cx.tcx());
                 let add = if stab.is_some() { " " } else { "" };
 
-                let doc_value = myitem.doc_value().unwrap_or_else(String::new);
+                let doc_value = myitem.doc_value().unwrap_or_default();
                 write!(
                     w,
                     "<tr class=\"{stab}{add}module-item\">\

src/librustdoc/passes/calculate_doc_coverage.rs

@@ -235,12 +235,7 @@ impl<'a, 'b> fold::DocFolder for CoverageCalculator<'a, 'b> {
                 let mut tests = Tests { found_tests: 0 };
 
                 find_testable_code(
-                    &i.attrs
-                        .doc_strings
-                        .iter()
-                        .map(|d| d.doc.to_string())
-                        .collect::<Vec<_>>()
-                        .join("\n"),
+                    &i.attrs.collapsed_doc_value().unwrap_or_default(),
                     &mut tests,
                     ErrorCodes::No,
                     false,